Chemical vapor deposition flow inlet elements and methods

ABSTRACT

A flow inlet element for a chemical vapor deposition reactor is formed from a plurality of elongated tubular elements extending side-by-side with one another in a plane transverse to the upstream to downstream direction of the reactor. The tubular elements have inlets for ejecting gas in the downstream direction. A wafer carrier rotates around an upstream to downstream axis. The gas distribution elements may provide a pattern of gas distribution which is asymmetrical with respect to a medial plane extending through the axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/150,091, filed on Jan. 8, 2014, which is a divisional of U.S. patentapplication Ser. No. 13/606,130, filed on Sep. 7, 2012, now U.S. Pat.No. 8,636,847, which is a divisional of U.S. patent application Ser. No.12/631,079, filed on Dec. 4, 2009, now U.S. Pat. No. 8,303,713, whichclaims the benefit of the filing date of U.S. Provisional PatentApplication No. 61/201,074, filed Dec. 4, 2008, the disclosures of whichare hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to chemical vapor deposition methods andapparatus.

BACKGROUND OF THE INVENTION

Chemical vapor deposition involves directing one or more gasescontaining chemical species onto a surface of a substrate, typically aflat wafer, so that the chemical species react and form a deposit on thesurface. For example, compound semiconductors can be formed by epitaxialgrowth of the semiconductor material on a crystalline wafer.Semiconductors referred to as III-V semiconductors commonly are formedusing a source of a Group III metal such as gallium, indium, aluminum,and combinations thereof and a source of a Group V element such as oneor more of the hydrides or of one or more of the Group V elements suchas NH₃, AsH₃, or PH₃, or an Sb metalorganic such as tetramethylantimony. In these processes, the gases are reacted with one another atthe surface of a wafer, such as a sapphire wafer, to form a III-Vcompound of the general formula In_(X)Ga_(Y)Al_(Z)N_(A)As_(B)P_(C)Sb_(D)where X+Y+Z=approximately 1, and A+B+C+D=approximately 1, and each of X,Y, Z, A, B, C and D can be between 0 and 1. In some instances, bismuthmay be used in place of some or all of the other Group III metals.

In certain processes, commonly referred to as a “halide” or “chloride”process, the Group III metal source is a volatile halide of the metal ormetals, most commonly a chloride such as GaCl₂. In another process,commonly referred to as metalorganic chemical vapor deposition or“MOCVD,” the Group III metal source is an organic compound of the GroupIII metal as, for example, a metal alkyl.

One form of apparatus which has been widely employed in chemical vapordeposition includes a disc-like wafer carrier mounted within thereaction chamber for rotation about a vertical axis. The wafers are heldin the carrier so that surfaces of the wafers face in an upstreamdirection within the chamber. While the carrier is rotated about theaxis, the reaction gases are introduced into the chamber from a flowinlet element upstream of the carrier. The flowing gases pass downstreamtoward the carrier and wafers, desirably in a laminar plug flow. As thegases approach the rotating carrier, viscous drag impels them intorotation around the axis, so that in a boundary region near the surfaceof the carrier, the gases flow around the axis and outwardly toward theperiphery of the carrier. As the gases flow over the outer edge of thecarrier, they flow downwardly toward exhaust ports disposed below thecarrier. Most commonly, this process is performed with a succession ofdifferent gas compositions and, in some cases, different wafertemperatures, to deposit plural layers of semiconductor having differingcompositions as required to form a desired semiconductor device. Merelyby way of example, in formation of light emitting diodes (“LEDs”) anddiode lasers, a multiple quantum well (“MQW”) structure can be formed bydepositing layers of III-V semiconductor with different proportions ofGa and In. Each layer may be on the order of tens of Angstroms thick,i.e., a few atomic layers.

Apparatus of this type can provide a stable and orderly flow of reactivegases over the surface of the carrier and over the surface of the wafer,so that all of the wafers on the carrier, and all regions of each wafer,are exposed to substantially uniform conditions. This, in turn promotesuniform deposition of materials on the wafers. Such uniformity isimportant because even minor differences in the composition andthickness of the layers of material deposited on a wafer can influencethe properties of the resulting devices.

Considerable effort has been devoted in the art heretofore todevelopment of flow inlet elements for use in apparatus of this type.Commonly, the flow inlet element has inlets for the reactive gasesdispersed over an active, gas-emitting area approximately equal in sizeto the wafer carrier. Some of these flow inlet elements carry the firstreactive gas, such as a mixture of a Group V hydride, whereas otherscarry the second reactive gas, such as a mixture of a metal alkyl and acarrier gas. These inlets may be formed as tubes extending parallel tothe axis of rotation, the inlets are distributed over thedownwardly-facing or downstream surface of the flow inlet element.Considerable effort has been devoted in the art heretofore to arrangingthe inlets in symmetrical patterns. Typically, the first gas inlets areprovided in a pattern which has radial symmetry about the axis ofrotation of the wafer carrier, or which has at least two perpendicularplanes of symmetry crossing one another at the axis of rotation. Thesecond gas inlets have been provided in a similarly symmetrical pattern,interspersed with the first gas inlets. The flow inlet element commonlyincorporates complex channel structures for routing the gases to thetubular inlets. Moreover, because the wafers typically are maintained ata high temperature as, for example, about 500° C. to about 1200° C., theflow inlet element must be provided with coolant channels. The coolantchannels carry a circulating flow of water or other liquid and thusmaintain the temperature of the flow inlet element relatively low, so asto limit or preclude premature reaction of the gases. As disclosed, forexample, in U.S. Published Patent Application No. 20060021574 A1, thedisclosure of which is hereby incorporated by reference herein, a flowinlet element may be provided with additional structures for dischargingflows of a carrier gas devoid of reactive species.

The carrier gas flows isolate the reactive gas flows from one anotherwhile the gases are in the vicinity of the flow inlet element. The gasesdo not mix with one another until they are remote from the flow inletelement. Moreover, discharging the carrier gas flows limits or preventsrecirculation of the reactive gases as they exit from the flow inletelement. Thus, the reactive gases do not tend to form undesired depositson the flow inlet element. As described, for example, in commonlyassigned U.S. Published Patent Application No. 20080173735 (now U.S.Pat. No. 8,152,923), the disclosure of which is hereby incorporated byreference herein, recirculation of the discharged gases in the vicinityof the flow inlet element may be reduced by providing blade-likediffusers projecting downstream from the surface of the flow inletelement to guide the gas flows.

Typically, the inlets are constructed and arranged to provide uniformflow velocity away from the flow inlet element over the entire activeregion of the flow inlet element, i.e., the entire area where the inletsare arranged. In some cases, the gas inlets for a particular gas may bepartitioned into two or more zones, as for example, a first zone nearthe axis of rotation and a second zone remote from the axis. These twozones may be provided with separate gas channels so that the flow ratesof the first gas can be controlled independently in the two regions. Forexample, in one common arrangement, the inlets for a first gas, such asa Group V hydride, are arranged in an array covering most of the flowinlet surface, whereas the inlets for a second gas, such as a Group IIIalkyl, are arranged in one or more narrow strips extending generallyradially with respect to the central axis. In such a system, a portionof a strip disposed remote from the axis supplies the second gas to aring-like portion of the wafer carrier having a relatively large area,whereas a portion of the same strip near to the axis supplies the gas toa ring-like portion of the wafer carrier having a smaller area. Toprovide equal flux of the second gas per unit area of the wafer carrier,it has been common to zone the second gas inlets to provide unequalrates of discharge of the second gas per unit length along the strip.For example, the inlets near the axis may be supplied with a gas mixturehaving a relatively low concentration of the second gas, whereas theinlets remote from the axis may be supplied with a more concentrated gasmixture. Such zoning adds to the complexity of the system.

Despite all of these developments, still further improvement would bedesirable.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention provides a chemical vapor depositionreactor. The reactor according to this aspect of the invention desirablyincludes a reaction chamber having upstream and downstream directions,and also desirably includes a carrier support adapted to support a wafercarrier at a carrier location within the reaction chamber for rotationabout an axis extending in the upstream and downstream directions. Thereactor according to this aspect of the invention preferably has a flowinlet element mounted to the chamber upstream of the carrier location,the inlet element having a gas distribution surface extending in X and Yhorizontal directions perpendicular to one another and perpendicular tothe downstream direction.

The flow inlet element desirably has a plurality of elongated gas inletsfor discharging gases into the chamber, the elongated gas inletsextending parallel to one another and across the gas distributionsurface in the X horizontal direction. The elongated inlets desirablyextend across a Y-direction medial plane of the reactor, and may extendacross the major portion of the gas distribution surface. For example,the elongated inlets may cover substantially the entire gas distributionsurface, or may cover an area approximately equal to the area of thewafer carrier. The elongated gas inlets preferably include a pluralityof first gas inlets for discharging a first reactive gas and a pluralityof second gas inlets for discharging a second reactive gas, the firstgas inlets being spaced apart from one another in the Y horizontaldirection, the second gas inlets being spaced apart from one another inthe Y horizontal direction and interspersed with the first gas inlets.

The flow inlets may be disposed in a in a pattern which is notsymmetrical about a medial plane of the reactor extending in the Xhorizontal direction. The pattern may be antisymmetrical about suchmedial plane. That is, for any first gas inlet disposed at a positive Ydistance to one side of the X-direction medial plane, a second gas inletis disposed at the corresponding negative Y distance to the oppositeside of the X-direction medial plane.

Still other aspects of the invention provide methods of vapor depositionand flow inlet elements for use in a vapor deposition reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sectional view depicting the depositionapparatus according to one embodiment of the invention.

FIG. 2 is a diagrammatic plan view of a component used in the apparatusof FIG. 1.

FIG. 3 is a diagrammatic sectional view taken along line 3-3 in FIG. 2.

FIG. 4 is a diagrammatic, partially sectional perspective view depictingcertain structures in the element of FIGS. 2 and 3.

FIG. 5 is a diagrammatic, partially sectional view of an enlarged scaleof a portion of the structure shown in FIG. 4.

FIG. 6 is a view similar to FIG. 5 but depicting a further portion ofthe structure shown in FIG. 4.

FIGS. 7, 8, and 9 are diagrammatic representations of gas distributionon a wafer carrier achieved with the apparatus of FIGS. 1-6.

FIG. 10 is a view similar to FIG. 4 but depicting portions of apparatusaccording to a further embodiment of the invention.

FIG. 11 is a further view similar to FIG. 4 but depicting apparatusaccording to yet another embodiment of the invention.

FIG. 12 is a view similar to FIG. 2 but depicting portions of apparatusaccording to yet another embodiment of the invention.

FIG. 13 is a diagrammatic sectional view of a component used in a stillfurther embodiment of the invention.

FIGS. 14, 15, and 16 are diagrammatic sectional views of components usedin still further embodiments of the invention.

DETAILED DESCRIPTION

A reactor according to one embodiment of the invention (FIG. 1) includesa reaction chamber 10 having walls with interior surfaces 11substantially in the form of surfaces of revolution about a central axis16. The reactor walls may include a tapering section 13 adjacent anupstream end of the reactor, and also may include a movable hoop-likesection 17. A spindle 12 is mounted in the chamber for rotation aroundaxis 16. A disc-like wafer carrier 14 is mounted on the spindle. Thewafer carrier 14 is arranged to hold one or more substrates, such aswafers 18, so that surfaces of 20 of the wafers face in an upstreamdirection U along the axis. Movable wall section 17 forms a shutterwhich extends around the wafer carrier 14 when the system is in anoperative condition as shown. The shutter can be moved axially to open aport for loading and unloading the system. Typically, the wafer carrier14 is detachably mounted on the spindle, so that the system can beunloaded by removing a wafer carrier and reloaded by inserting a newwafer carrier.

A heater 15 such as an electrical resistance heater is provided withinthe reactor for heating the wafer carrier and wafers. Also, an exhaustsystem 19 is connected to the downstream end of the reaction chamber.

The foregoing features of the apparatus may be similar to those used inreactors sold under the trademarks “TurboDisc” and “Ganzilla” by VeecoInstruments, Inc. of Plainview, N.Y.

A flow inlet element 22 is provided at the upstream end of the reactionchamber. A downstream surface 24 of the flow inlet element faces in thedownstream direction, toward the wafer carrier and wafers. The flowinlet element is connected to a source of a first reactive gas 30, suchas a Group V hydride, typically in admixture with a carrier gas such asN₂ or H₂. The flow inlet element is also connected to a source 26 of asecond reactive gas, such as a metal alkyl, also typically in admixturewith a carrier gas. Additionally, the flow inlet element is connected toa source 32 of a carrier gas such as N₂ or H₂, which is not admixed withany reactive gas, and to a coolant circulation device 33.

As best seen in FIGS. 2 and 3, flow inlet element 22 includes a topplate 40 having a downstream-facing surface 42 and an annular manifold44 projecting downstream from the downstream surface 42. Manifold 44 issubdivided by internal baffles 46 (FIG. 2) into a first gas section 48and a second gas section 50. The first gas section 48 and second gassection 50 lie generally on opposite sides of a medial plane 52 whichextends through and incorporates the axis 16 of the reactor. The firstgas section 48 is connected to the source of first reactive gas 30,whereas the second gas section 50 is connected to the source of thesecond reactive gas 26 (FIG. 1). These connections may be establishedthrough bores extending downwardly through the top plate 40. An annularcoolant channel is provided downstream from the gas manifold 48. Thecoolant channel is subdivided into a coolant inlet section 54 disposedon one side of medial plane 52, and a coolant outlet section 56 disposedon the opposite side of medial plane 52.

The coolant inlet and outlet sections are connected to the coolantcirculation apparatus 33 (FIG. 1) by conduits (not shown) extendingthrough the manifold sections 48 and 50.

A gas distribution plate 60 is disposed downstream from the top plate 40so that plates 60 and 40 cooperatively define a gas distribution chamber62 between them. The gas distribution chamber 62 communicates with thecarrier gas source 32 (FIG. 1), but does not communicate with the firstor second gas sections of the manifold.

As best seen in FIG. 4, plate 60 is formed from numerous elongatedtubular gas distribution elements 64 and 66 extending parallel to oneanother. The direction of elongation of the elongated elements 64 and 66is arbitrarily referred to as the “+X” direction. This direction is adirection perpendicular to the upstream and downstream directions, andperpendicular to the axis 16 of the chamber (FIG. 1). The elongatedelements are offset from one another in a “+Y” direction, which is alsoperpendicular to axis 16 and perpendicular to the +X direction.

Directions perpendicular to the axis 16, including the X and Ydirections, are referred to herein as “horizontal” directions inasmuchas axis 16 normally (although not necessarily) extends vertically in thenormal gravitational plane of reference. Also, planes which areperpendicular to the axis are referred to herein as horizontal planes.Thus, both top plate 40 and distribution plate 60 extend in horizontalplanes. Also, the horizontal direction opposite to the +X direction isreferred to herein as the −X direction, and the direction opposite tothe +Y direction is referred to herein as the −Y direction, in theconventional manner of a Cartesian coordinate system. The upstream anddownstream directions U and D, parallel to axis 16 constitute the thirdor Z direction of the Cartesian coordinate system.

Tubular elements 64 are referred to herein as first gas distributionelements. As thus seen in FIG. 5, each first gas distribution elementincorporates a generally rectangular tubular body having a solidupstream wall 68, solid side walls 70, and a downstream wall 72. Walls68, 70, and 72 cooperatively define an interior bore 74. The downstreamwall 72 has an opening in the form of an elongated slot 76 extendingthrough the wall. Slot 76 extends lengthwise (in the X direction) alongthe first gas element 64.

An elongated diffuser 78 is mounted on the downstream wall 72 andextends lengthwise along the first gas distribution element 64. Diffuser78 is generally in the form of a triangular prism. The diffuser isformed from two sections 80, each of which incorporates a passageway 82extending lengthwise within the diffuser, i.e., in the X directions.Sections 80 are mounted back to back on the downstream wall 72 of thetubular element. Diffuser 80 as a whole is generally in the form of anelongated triangular prism. The width or dimension of the diffuser inthe Y directions decreases with distance in the downstream direction Daway from the tubular elements. A passageway or additional gas inlet 84extends through the diffuser 78 from the tubular element to the edge ofthe diffuser remote from the tubular element, i.e., the downstream edgeof the diffuser. The passageway or inlet 84 is in the form of anelongated slot defined by the two back-to-back triangular sections 80 ofthe diffuser. Passageway 84 communicates with slot 76 and hence with theinterior bore 74 of the tubular element along the length of the firstgas distribution element 64.

Elements 66, referred to herein as second gas distribution elements, areidentical to the first gas elements 64, except that the downstream wall86 of each second gas distribution element (FIG. 6) has a series ofholes 88 arranged along the length of the element instead of the slot 76of the first gas distribution elements. Also, the diffuser 90 of eachsecond gas distribution element has a series of small tubular inletports 92, one of which is visible in FIG. 6 extending through thediffuser and communicating with the holes 88. Each of the passages orinlet ports 92 is open at the downstream edge of the diffuser 90. Hereagain, each tubular element has an upstream wall 96 and sidewalls 94 sothat the downstream wall 86 and the other walls 94 and 96 cooperativelydefine an interior bore 98 extending lengthwise within the element. Hereagain, each diffuser has coolant passages 100, also extendinglengthwise. The numerous individual inlets 92 provided along the lengthof element 66 cooperatively define an elongated inlet. Thus, as used inthis disclosure, references to an elongated inlet should be understoodembracing both an elongated unitary slot such as the slot 76 of element64, and also embracing an elongated inlet formed from plural individualinlets arranged in a row.

As seen in FIG. 4, the first and second gas distribution elements 64 and66 are arranged side by side and are mechanically attached to oneanother as by welds 102 extending between the sidewalls 94 and 70 ofmutually adjacent elements. The upstream walls 94 and 68 of the elementscooperatively define an upstream surface of the plate 60, whereas thedownstream walls 72 and 86 cooperatively define the downstream surfaceof the plate. The welds 102 are arranged only at spaced-apart locationsalong the lengths of the elements. Thus, slot-like inlet openings 104,referred to herein as “base” inlets, extend through the plate from itsupstream surface to its downstream surface, between the adjacent gasdistribution elements 64 and 66. The upstream surface of the gasdistribution plate 60 confronts the space 62 between plate 60 and topplate 40.

As best seen in FIGS. 2 and 3, the composite plate 60 is mounted to themanifold 44 and extends entirely across the circular area enclosed bythe manifold. Thus, plate 60 entirely occupies a circular regionreferred to herein as the active or gas-emitting region of the flowinlet element. This circular region is coaxial with axis 16. The firstgas distribution element 64 and second gas distribution element 66extend in the X horizontal directions, i.e., the directions parallel toa medial plane 108 which also extends in the X direction. The first andsecond gas distribution elements 64 and 66 extends physically betweenthe first gas section 48 and second gas section 50 and are mechanicallyconnected to both sections, as for example, by welding. However, theinterior bores of the first gas distribution elements 64 communicateonly with the first gas section 48, whereas the interior bores of thesecond gas distribution elements 66 communicate only with the second gassection 50. The coolant channels 82, 100 (FIGS. 5 and 6) incorporated inthe diffusers 78, 90 are open at both ends and are connected to thecoolant inlet section 54 and coolant outlet section 56 (FIG. 3).

As best seen in FIG. 2, each of the individual gas distribution elements64 and 66 extends in the X direction across the medial plane 52 whichextends perpendicular to the X direction. The elongated inlets definedby the individual gas distribution elements also extend across medialplane 52. In this embodiment, each gas distribution element, and theelongated inlets defined by each gas distribution element, extendsacross substantially the entire span of the active gas distributionregion of the flow inlet element. The first and second gas distributionelements 64 and 66 are not arranged symmetrically with respect to themedial plane 108 extending in the X direction. Rather, the first andsecond gas distribution elements 64, 66 are arranged within anantisymmetrical or negative-symmetry pattern with respect to medialplane 108. That is, for each first gas distribution element 64 arrangedat a positive or +Y difference from medial plane 108, there is a secondgas distribution element 66 arranged at the corresponding −Y distancefrom medial plane 108. For example, first gas distribution element 64 ais disposed at distance +Y_(a) from medial plane 108. Second gasdistribution element 66 a is disposed at the corresponding, negativedistance −Y_(a) of equal magnitude from the same medial plane. Thedistance to each gas distribution element is measured to thelongitudinal center line of the inlets defined by such element as, forexample, the longitudinal center line of slot-like inlets 84 (FIG. 6) orthe longitudinal center line of the rows of holes 92 (FIG. 6). In thedepiction of FIG. 2, the spaces or base gas inlets 104 between the gasdistribution elements are omitted for clarity of illustration.

In operation, a first reactive gas such as a mixture of ammonia or otherGroup V hydride in admixture with one or more carrier gases such as H₂,N₂ or both is supplied through the first gas section 48 of the manifoldand passes into the longitudinal bores 74 (FIG. 5) of the first gasdistribution elements 64. The first reactive gas thus issues as a seriesof elongated, curtain-like streams of gas 111 (FIG. 4) from the inlets34 defined by the first gas distribution elements 64 and associateddiffusers 78. Similarly, a second reactive gas, such as a metal alkyl inadmixture with a carrier gas, is supplied through the second gas section50 (FIG. 2) of the manifold and passes through the interior bore 98(FIG. 6) of the second gas distribution element 66. The second gas thusissues as rows of streams 113 (FIG. 4) from the inlets 92 defined by thesecond gas distribution elements and the associated diffusers. Theserows of gas streams 113 are interspersed between the streams 111 of thefirst gas. A carrier gas such as H₂, N₂ or a mixture thereof isintroduced into the carrier gas space 62 and passes through the spacesor base openings 104 defined between the gas distribution elements 64and 66 constituting the plate. The carrier gas thus issues ascurtain-like streams 115 interposed between each stream 111 of the firstreactive gas and the adjacent rows of streams 113 of the second reactivegas. The streams of gases travel downstream to the vicinity of the wafercarrier 14 and the wafers 18, where they are swept into rotational flowby the rotational motion of the wafer carrier and wafers. The first andsecond reactive gases react with one another at the wafer surface toform a deposit as, for example, a III-V semiconductor.

The first and second reactive gases remain substantially separate fromone another while they are in the vicinity of the flow inlet element andflow downstream from the flow inlet element in a substantially laminar,orderly flow. Several factors contribute to this action. The diffusers90 and 76 define generally V-shaped channels between them, such channelsbeing disposed downstream of the base inlets 104. The channels broadengradually in the Y horizontal direction with distance downstream fromthe base inlets 104. This facilitates spreading of the carrier gas flows115 in an orderly fashion, so that a substantially laminar carrier gasflow prevails at the downstream edges of diffusers 76 and 90. The firstand second reactive gas flows 111 and 113 are introduced into this flowregime at the downstream edges of the diffusers and thus tend to flow ina similar orderly laminar flow. Moreover, the carrier gas flows 115provide substantially complete isolation between the first reactive gasflows 111 and the second reactive gas flows 113. Stated another way, apath in a horizontal plane, transverse to the upstream-to-downstreamaxis 16, which path extends from one of the second reactive gas flows113 to an adjacent first reactive gas flow 111 would intercept one ofthe carrier gas flows 115. This is true for any curve drawn in ahorizontal plane, which is confined within the active area of the flowinlet element, i.e., the area where gas inlets are present. Thissubstantially complete isolation between the first and second reactivegas flows minimizes premature reaction between the gases.

The flows of first and second gases are not symmetrical about the medialplane 108 extending in the X direction. If the wafer carrier and waferswere static, this would result in nonuniform exposure of the wafercarrier and wafers to the first and second reactive gases. For example,as schematically depicted in FIG. 7, a wafer carrier 14 is shown with amarker 120 on the carrier provided for purposes of illustration pointingin the +X direction, to the right in FIG. 7. If the wafer carrier wereto remain in this orientation, the region shown as dark stripes would beheavily impacted by the first reactive gas, whereas the region shown aslight stripes would be more heavily impacted by the second reactive gas.The same pattern of impact areas is shown in FIG. 8, but with the wafercarrier 14 rotated 180° about the central axis 16, so that the indicator120 points in the opposite or −X direction. The pattern of light anddark stripes in FIG. 8 is the reverse of the pattern in FIG. 7. Thus, asthe wafer carrier rotates, the regions which were heavily exposed to thefirst gas in one orientation of the wafer carrier will be heavilyexposed to the second gas in the opposite orientation of the wafercarrier. With continual rotation of the wafer carrier, the exposurepattern becomes uniform as shown in FIG. 9.

In this arrangement, each unit length along one of the elongated firstgas distribution elements 64 (FIG. 2) supplies the first gas to an areaof the same size on the wafer carrier. Likewise, each unit length alongone of the elongated second gas distribution elements 66 (FIG. 2)supplies the second gas to an area of the same size on the wafercarrier. Therefore, substantially uniform flux of the first and secondgases on the wafer carrier can be provided if all of the first gasdistribution elements 64 are arranged to the same mass flow rate of thefirst gas per unit length along their entire lengths, and all of thesecond gas distribution elements 66 are arranged to provide the samemass flow rate of the second gas per unit length along their entirelengths. The mass flow rate of the first gas per unit length desirablyis uniform over the entire length of each elongated slot 84 (FIG. 5).Also, the mass flow rate of the second gas desirably is uniform over theentire length of each elongated inlet defined by a row of discreteinlets ports 92 (FIG. 6). There is no need to provide multiple zones offirst gas inlets or multiple zones of second gas inlets with differentvolume flow rates per unit length or different concentrations of thefirst or second gasses. This significantly simplifies the constructionand operation of the system. Moreover, such simplicity is providedwithout the complex structures commonly used to provide uniform arraysof gas inlets. To assure that the mass flow rate is uniform along thelength of each flow inlet element 64 or 66, the flow resistance alongthe length of the element, through bore 74 or 98, desirably is small incomparison to the flow resistance from the bore through inlets 84 and92.

It should be appreciated that the impact patterns shown in FIGS. 7 and 8are schematic patterns provided for illustration only. In actualpractice, the gases flowing downstream themselves are swept intorotational motion about the axis. The rotational motion of the gasestends to make the pattern of exposure to the gases at any givenrotational position of the wafer carrier more uniform than those shownin FIGS. 7 and 8.

The structure and method of operation discussed above can be utilized inreaction chambers of essentially any size. The structure can be scaledup to relatively large sizes as, for example, reactors having a wafercarrier of about 600 mm or more and having a flow inlet element with anactive, gas-emitting region of approximately the same diameter or more.Moreover, the flow inlet element can be fabricated readily.

Numerous variations and combinations of the structures discussed abovecan be employed. In a variant of the arrangement discussed above, thefirst gas distribution elements 64 may be used to supply flows ofcarrier gas, whereas the base inlets 104 may be used to supply flows ofa reactive first gas and the second gas distribution elements may beused to supply a reactive second gas. In still other variants, more thantwo reactive gasses may be used. For example, the gas distributionelements may include first, second and third gas distribution elementsextending generally parallel to one another.

In a further variant shown in FIG. 10, the gas space 262 between the gasdistribution plate 260 and the top plate 240 of the flow inlet elementis connected to the source of first reactive gas as, for example,ammonia, so that the flows of gas issuing through the base inlets 204between the gas distribution elements of the plate are flows 111 of thefirst reactive gas. In this embodiment, all of the gas distributionelements 266 constituting plate 260 are configured in the same way asthe second gas distribution elements 66 discussed above. Thus, flows 113of the second reactive gas issue from the additional inlets 274 at theedges of all of the diffusers. In other variants, all of the flow inletelements are configured with slit-like inlets such as those used in thefirst gas distribution elements 64 discussed above. Even where noseparate carrier gas flow is used to provide separation between thefirst and second gases, ejection of the second reactive gas 113 at thetips of the diffusers, within the smooth flow laminar of first reactivegas 111 facilitated by the diffusers provides good reassurance againstrecirculation of the gases and deposition of unwanted by-products on theflow inlet element.

In another embodiment (FIG. 11), each gas distribution element includesa tubular body 286 which defines an elongated gas inlet in the form of arow of holes 287 open at the downstream face of the tubular body. Eachelongated gas distribution element has two diffusers 288 mounted to thedownstream face of the tubular body so that the two diffusers lie onopposite sides of the elongated inlet. Here again, the gas distributionelements are attached to one another but spaced apart from one anotherso as to define base inlets 290 between them. In this embodiment, theinlets defined by the rows of holes 287 in the gas distributionelements, as well as the base inlets 290 open to the reaction chamber atthe downstream surfaces of the tubular bodies 286, so that the openingsof the all of the inlets are disposed in the same plane. In thisarrangement, a diffuser 288 is disposed between each inlet 287 definedby the gas distribution element and the adjacent base inlet 290. Hereagain, the gas space 292 between the top plate 240 and the compositeplate formed by the gas distribution elements is connected to a sourceof a first gas, whereas the gas distribution elements are connected to asource of a second gas, so that first gas flows 111 issue from the baseinlets 290 and second gas flows 113 issue from the inlets 287 defined bythe gas distribution elements. In this embodiment as well, the smoothlaminar flow facilitated by the diffusers inhibits recirculation anddeposit formation. In this embodiment as well, the diffusers desirablyare provided with coolant passages 289. In further variants, some or allof the elongated inlets defined by the gas distribution elements may beslots rather than rows of holes. Here again, the gases may include acarrier gas in addition to the first and second gases.

In yet another variant, the diffusers mounted on the downstream surfaceof the gas distribution plate may be omitted. In a still furthervariant, a porous screen may be provided over the downstream surface ofthe composite plate except at the inlets. In yet another arrangement(FIG. 12), the tubular gas distribution elements 360 are mounted side byside in abutting relationship with one another and fastened together as,for example, by welding. In this arrangement, there are no base inletsextending through the gas distribution plate formed by the gasdistribution elements 366. A porous screen 300 is mounted downstreamfrom plate 360, and the inlets 364 of the various gas distributioninlets are provided with short tubes extending downstream through thescreen. A carrier gas may be introduced into the space 363 between thecomposite plate 360 and the screen 300, so that the carrier gas flowsthrough the screen and surrounds each of the streams of reactive gasesissuing from the inlets 362. Cooling channels 367 may be provided inthis embodiment on the bottom surfaces of the individual gasdistribution elements.

In the embodiments discussed above, the gas distribution plate is formedfrom separate elongated gas distribution elements joined to one another.However, the gas distribution plate also can be formed from one or moreunitary plates defining elongated inlets similar to those discussedabove.

In the embodiments discussed above, the elongated gas inlets arestraight. However, this is not essential. For example, in the embodimentof FIG. 13, each elongated first gas inlet 464, representedschematically by a solid line, extends in a zig-zig pattern. Thus, eachsuch inlet extends generally in the X directions, with minor deviationsin the Y direction. The elongated second gas inlets 466, representedschematically by broken lines, extend in a similar zig-zag pattern. Thebase inlets (not shown) may also have a similar zig-zag configuration.In this arrangement as well, the first and second gas inlets extendgenerally parallel with one another. However, each elongated gas inletstill extends generally in the X direction. Stated another way, over anysubstantial extent Ex of a gas inlet in the X directions, the extent ofsuch inlet Ey in the Y direction is small in comparison to Ex. In afurther variant (FIG. 14), the elongated gas inlets 564 and 566 are inthe form of arcs rather than straight lines. Here again, the gas inletsextend generally in the X direction.

In the embodiments discussed above, each elongated gas inlet providesthe same mass flow rate of a reactive gas per unit length along itsentire length. In a variant, the mass flow rate of the reactive gas perunit length may vary progressively along the length of the elongated gasinlet. This may occur, for example, where a particular elongated gasdistribution element receives a gas mixture at only one end, and hasappreciable resistance to flow along its length. FIG. 15 schematicallydepicts the impact pattern 601 a of a first reactive gas flowing fromsuch an elongated inlet. In this case, the mass flow rate of thereactive gas from the particular inlet diminishes progressively in the+X direction along the length of the inlet. Thus, the breadth of thearea on the wafer carrier impacted by the gas is shown as diminishing inthe +X direction. In the arrangement of FIG. 15, the second reactive gasinlets 606 have mass flow rates which diminish in opposite, −Xdirection. Rotation of the wafer about the central axis will cancel outthe differences in the impact patterns. For example, a portion of thewafer which is aligned with portion 603 of impact pattern 601 a will bealigned with portion 605 when the wafer carrier rotates one half turn.In yet another arrangement, alternate ones of the first gas inlets mayhave mass flow rates, and hence impact patterns, which diminish inopposite X directions. The second gas inlets may have a similararrangement.

In the embodiments discussed above, the first and second gas inlets areprovided in equal number and arranged in 1:1 alternating order in the Ydirection. However, this is not essential. For example, 2, 3 or moreelongated first gas inlets may be provided between each pair of secondgas inlets.

Also, it is not essential to place the elongated gas inlets in exactanti-symmetrical arrangement about the medial plane extending in the Xdirection. Deviations from this arrangement, up to and including asymmetrical arrangement, can be used. Also, in the embodiments discussedabove, the plate defining the elongated gas inlets includes elongatedtubular gas distribution elements. However, elongated gas inlets may beprovided by other structures as, for example a one or more unitaryplates having appropriate gas distribution channels or chamberscommunicating with the inlets.

A chemical vapor deposition apparatus according to a further embodimentof the invention (FIG. 16) includes a reaction chamber 710 which isgenerally in the form of a hollow body of revolution about a centralaxis 716. As in the embodiment discussed above with reference to FIG. 1,the apparatus includes a support such as a spindle (not shown) adaptedto support a wafer carrier (not shown) for rotation about central axis716. In this embodiment, the flow inlet element 722 defines first gasinlets 764, represented schematically by solid lines in FIG. 16, andsecond gas inlets 766, represented schematically by dashed lines. Thefirst gas inlets are connected to a source of a first reactive gas, as,for example, a gas mixture containing a Group III element, whereas thesecond gas inlets are connected to a source of a second gas reactivewith the first gas, such as a gas mixture containing a Group V element.The gas inlets also include third gas inlets 768, schematically shown asdotted lines in FIG. 16. The third gas inlets are connected to a sourceof a carrier gas which is substantially non-reactive with the first andsecond gases under the conditions prevailing within the chamber.

The first gas inlets extend only within a region of the gas distributionsurface having a first radius R₁ from the central axis 716. Statedanother way, the first gas outlets extend to a first radius R₁ from thecentral axis. The second gas outlets extend to a second radius R₂ fromthe central axis, which in this embodiment is equal to the first radiusR₁. The third gas inlets extend to a radius R₃ which is greater than thefirst and second radii, and hence greater than R₁ and R₂. In theparticular example depicted, the radius R₃ is equal to, or just slightlyless than, the interior radius of the reaction chamber at the gasdistribution surface. The first and second radii R₁ and R₂ may beapproximately equal to the radius of the wafer carrier.

In operation, the gasses issuing from the first and second gas inletswill pass downstream (in the direction along axis 716 toward the viewerin FIG. 16) to the wafer carrier and participate in chemical vapordeposition reactions or other treatment of the wafers carried on thecarrier. In the region within first and second radii R₁ and R₂, thecarrier gas issuing from the third gas inlets passes downstream betweenthe streams of first and second gasses, and maintains separation betweenthese streams for at least part of the distance from the flow inletelement to the wafer as discussed above. In the gap region G outside ofthe region occupied by the first and second gas inlets, the carrier gasissuing from the third gas inlets forms a curtain which keeps thereactive first and second gasses isolated from the wall of chamber 710.This minimizes deposition of reaction products on the chamber walls. Inparticular, recirculation of gases can occur at the upstream end of thechamber where the flow inlet element 722 joins the reactor wall. Withthe arrangement shown in FIG. 16, any recirculating gases will becomposed essentially of the carrier gas, and therefore will not tend toform deposits on the reactor walls or flow inlet element.

Moreover, omission of the first and second inlets in the gap region Greduces the required total flow of the first and second reactant gasesto maintain a given flux of reactants toward the wafer carrier. Statedanother way, if first and second reactive gasses were provided in thegap region G, they would simply pass around the outside of the wafercarrier, without ever impinging on the wafers. Avoiding this wastereduces the cost of reactant gases used in the process, and also reducesdischarge of waste reactant gases.

The arrangement shown in FIG. 16 may be varied. For example, the firstand second radii R₁ and R₂ may differ from one another. One of theseradii may be as large as, or even greater than, the third radius R₃. Insuch an arrangement, the curtain of gas adjacent the reactor wall wouldinclude the carrier gas and only one of the reactant gases. Such acurtain would still be effective to suppress deposition at the chamberwall. It is not essential to provide third gas inlets between the firstand second gas inlets. For example, the third gas inlets may be providedonly in the gap region G. Also, the gas inlets are shown in FIG. 16 asdisposed in parallel rows, but other configurations can be used. Forexample, the first gas inlets can be in the form of a “field” orcontinuous area, whereas the second gas inlets can be in the form of oneor more radial rows.

As these and other variations and combinations of the features discussedabove can be utilized without departing from the present invention, theforegoing description of the preferred embodiments should be taken onlyby way of illustration and not by way of limitation of the presentinvention.

INDUSTRIAL APPLICABILITY

The present invention can be applied, for example, in manufacture ofsemiconductor devices.

1. A method of chemical vapor deposition comprising the steps of: (a)maintaining a wafer carrier holding one or more wafers within a reactionchamber so that surfaces of the wafers face in an upstream direction;(b) rotating the wafer carrier around an axis extending in the upstreamand downstream directions; and (c) discharging a plurality of gassesdownstream toward the wafer carrier from a plurality of elongated gasinlets extending parallel to one another in a first horizontal directiontransverse to the axis, the discharging step being performed so thatstreams of first and second reactive gases are discharged from separateones of the elongated inlets and so that a carrier gas carrier gassubstantially devoid of the first and second reactive gasses andsubstantially nonreactive with the first and second reactive gasses isdischarged from other ones of the reactive inlets and so that at leastsome of the streams of carrier gasses are discharged between adjacentstreams of first and second carrier gasses.
 2. A method as claimed inclaim 1 wherein the first reactive gas includes one or more sources ofone or more Group III metals and the second reactive gas includes andone or more sources of one or more Group V elements.
 3. A method ofchemical vapor deposition comprising: (a) rotating a disc-like holdercarrying the substrates about an axis while maintaining surfaces of thesubstrates substantially perpendicular to the axis and facing in anupstream direction along the axis; and, during the rotating step, (b)discharging first and second gasses reactive with one another in adownstream direction parallel to the axis toward the substrates as firstand second sets of gas streams extending to first and second radialdistances from the axis, respectively, and simultaneously discharging athird gas substantially non-reactive with the first and second gases inthe downstream direction as a third set of gas streams extending to athird radial distance from the axis greater than at least one of thefirst and second radial distances.